Ah, the beauty of photoluminescent ginkgo leaves

Etched on a photoluminescent display, these liquid crystal ginkgo leaves can shift through a trio of autumn colours under the glow of UV light. Previously, displays made from a single luminescent organic or organometallic compound could only switch between two colour states. Now Takashi Kato and Yoshimitsu Sagara of the University of Tokyo have developed a reversible display that glows red-orange, green or yellow in response to temperature and mechanical force.

The display consists of a mixture of two compounds, one of which harbours a fluorescent centre. When the mixture is heated to 146°C and then cooled to room temperature, it forms the red-orange state. A summer green appears after heating the red-orange colour state to 90°C, applying mechanical shear with a spatula, and then cooling it back to room temperature. Either the red-orange or green states can revert to yellow by shearing the mixture at room temperature.

The findings could be used to develop more cost effective multicolour displays.